Research Of Impact To Signal Transmission Of Contact Surface Pollution

To investigate the effects of the corrupted electric contact surface in communication system, the electrical properties of electric contact surfaces, the situations of the electric contact surfaces be corrupted and its effects to signal transmission should be studied here. This paper focuses on the high frequency properties of electric contacts, especially the variations of high frequency contact impedance and the degradation of system performance owing to the corruption of the electric contact surfaces. A model of electric contact impedance in digital communication systems was set up and some theoretical analyses were carried out. Some field and simulation experiments were conducted too. The research work and results are summarized and shown as follows:Analyze the situation of the plating quality of the connectors from DDF(Digital Distribution Frame) on line. The study reveals that some connectors'quality degradations exist. Scratches and crackles or tears were discovered on some contact surfaces; the quality of gold plating was poor so the plating thickness was under desired and the number of pores and defects was high—the anti-wear ability was under desired too. At the mean time, corruption products and dust deposition can be seen on majority contact surfaces, and the pollution degree of some surfaces was severe. The existence of dust particles and corruption products on electric contacts was an important factor to threaten the connector performance and the transmission signal reliability in communication system.Study the high frequency properties of electrical contact and electrical contact interface. Set up models of single-spot contact and multi-spot contact to analyses the high frequency parameters theoretically, and further more to analyses the variations to those parameters from degradated contacts of environmental pollution. The body inductance and resistance of electric contacts, the contact resistance and contact capacitance of electric contacts, and etc. so many parameters were all the functions of frequency used, and were related to the pollution condition of contact surfaces.Theoretical analyses on the affection to signal transmission performance of electric contact. At first, from traditional transmission line theory, the existence of connectors in transmission line introduces impedance discontinuity and causes signal reflection and loss; second, from the equivalent circuit of electric contact, the existence and variation of contact impedance from the contact spot (or region) can also result in signal transmission loss, and even more, if not terminal impedance matched, can also lead multi-reflections and intensify the loss of signal integrity.Experimental research about the contact properties of polluted surfaces, involved the microscope observation of surface corroded products and measurements of high frequency impedance on various contact surfaces (such as gold-plating, silver plating and dust deposition surfaces), to reveal the effect to signal transmission from polluted surfaces. Long term natural exposure gold plating coupon related the microstructure of polluted surface to the high frequency performance of the electric contact; the measurement of contact property of silver plating coupon indicated frequency characteristic of corrupted film on coupon surface; finally, laboratory accelerated dust deposition coupon's research reflected the link of contact force and contact impedance.Experimentally study the influence to electric contact body's frequency properties of surface pollution. Using lumped parameter model, the relationship of inductance, resistance of electric contact parts to signal frequency used and surface pollution condition were measured.